Dense foams have been used as sealing elements in packers where they are called on to withstand pressure differentials while sealing off one zone in a borehole from another. U.S. Pat. No. 7,216,706 shows in FIG. 26 a foam sleeve used as a packer over a tubular that is expanded as described in columns 19 and 20. US 2005/0103493 FIGS. 4 and 5 illustrate a plug with a foam exterior that can get around obstructions before landing, see paragraph 41.
In other applications foam can be pumped into a borehole to bring with it to the surface the debris that is encountered when the foam is released. US 2005/0217854 shows circulating foam to remove debris, see FIG. 2a and paragraphs 37-39.
In yet other applications unrelated to subterranean operations, foam can be used as a structural material such as in a roll assembly or to protect space vehicles from flying debris. US 2008/0145591 shows a roll with foam core. U.S. Pat. No. 6,206,328 uses foams as an external barrier from flying objects that can strike a space vessel.
None of these uses of foam address the present invention. There are numerous situations where movable components in tools used in subterranean locations are in debris-laden environments and there are movable parts that create an open void space when in one position and move to reduce the volume of that void space when actuated into another position. In some applications there can be a long time between such movements and during that time the debris that comes off tubing walls or is carried in the drilling mud or by cuttings generated from milling or drilling and during that time such debris can get into such voids so that when it is time to actuate the tool component it will not move fully or at all because of a buildup of debris. The component could also jam on the debris after moving just a part of its needed range of motion. In other applications, notably in gravel packing where there are seal bores that are potential collection locations for debris and the gravel has to make a lateral exit when deposited it is advantageous to keep the gravel or proppant out of not only the seal bores but also from the locations that are below. At the same time it would also be significant to allow hydrostatic pressure to be communicated through such a debris barrier so that pressure differentials do not tear it out of its position. In such applications the foam annular cylindrical shape can be used around an inner string for positioning in a gravel packing bottom hole assembly so that the delivered debris stays out of locations where it can collect and affect the operation of downhole equipment. In such applications, the foam shape would not be significantly compressed. In other applications where the foam is inserted into a void whose volume needs to be reduced when parts are actuated to move, there is a need for the foam or other selected material to be able to compress to accommodate part movement. While some infiltration of the void space is envisioned the mass of the foam or other material still needs to be able to compress enough to allow part movement of the surrounding tool.
Those skilled in the art will more readily appreciate other aspects of the invention from a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be found in the appended claims.